JP2009221578A - Method of continuously annealing steel strip having curie point and continuous annealing apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of continuously annealing a steel strip with which the steel strip having Curie point can be annealed at temperature rising speed uniform in the longitudinal direction. <P>SOLUTION: The continuous annealing apparatus is provided with: a first heating device with which the steel strip is heated to ≥500°C and <the Curie point Tc(°C)-50°C, in a first heating area; a solenoid-coil type high frequency induction-heating device with which the steel strip heated in the first heating area, is heated to the temperature range of the Curie point Tc-30°C to the Curie point Tc-5°C, in a second heating area; a third heating device with which the steel strip heated in the second heating area, is heated to a treating target temperature exceeding the Curie point, in a third heating area; and a temperature rising speed controlling device with which the heating action of the first heating device and the induction-heating device are controlled. An electric current output value is set to the induction-heating device in the second heating area and also, on the basis of this actual result output electricity value, a fuel gas output value for outputting to the first heating device and/or electric power output value of an electric heater, are controlled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a continuous annealing method and a continuous annealing facility for a steel strip having a Curie temperature (also referred to as Curie Temperature: Tc), and is particularly suitable for use in controlling the temperature rising rate in the vicinity of the Curie temperature. It is about technology. In addition, as the steel strip having the Curie point to be processed by the continuous annealing method and the continuous annealing equipment of the present invention, a grain-oriented electrical steel sheet containing Si ≦ 4.5 mass% can be exemplified.

  In continuous annealing of a metal strip such as a steel strip, the heating temperature, the heating time, the heating rate, etc. are generally strictly controlled. Among them, for example, strict heating rate control may be required as in the decarburization annealing process in the manufacturing process of the low iron loss directional electrical steel sheet suitable for use as an iron core of a transformer or other electrical equipment. .

  In the manufacture of grain-oriented electrical steel sheets, (a) in the temperature rising process during decarburization annealing, the steel sheet temperature at which the steel sheet undergoes strain recovery and recrystallization is present in the vicinity of the Curie point from 550 ° C. It is important to heat at a constant rate of heating while it is present. Outside this region, the grain structure after decarburization annealing has a large ratio of {111} planes, and as a result, there arises a problem of causing a decrease in magnetism. In addition, (b) a problem that the film is deteriorated due to variations in the heating rate occurs.

  As an invention relating to the management range of such annealing temperature increase rate, Patent Document 1 discloses that a steel strip that has been cold-rolled is 705 ° C. at a heating rate of 230 ° C./second or more during decarburization annealing of a grain-oriented electrical steel sheet. Inventions that can improve iron loss by rapid heating to the above temperature are disclosed. In Examples 2 and 3, a special electromagnetic induction for heating to a Curie point of 746 ° C. at a heating rate of 1100 to 1200 ° C./sec. The use of a heating coil (fundamental frequency: 450 kHz) is disclosed.

  In addition, regarding the continuous annealing method for steel sheets, an induction heating device is used to change the plate temperature of the condition change part in order to smoothly change the annealing conditions from the preceding material to the subsequent material having different annealing conditions. The invention to be utilized is disclosed in Patent Document 2.

  In addition, Patent Document 3 relates to tempering using a plurality of induction heating devices for a steel sheet, actually measuring the temperature of the leading portion of the steel material on the entry side of the device, determining the power required for heating, and setting the power, Alternatively, an invention is disclosed in which a thermometer is installed between the induction heating devices, the steel material temperature is measured, the power setting value is corrected, and the material uniformity in the longitudinal direction of the steel sheet is achieved.

  Further, in Patent Document 4, when accelerated cooling is employed in a thick steel plate manufacturing process, variations in the mechanical properties and shape defects of the steel plate caused by temperature irregularities that are likely to occur due to its high cooling property, and further residual stress. In the steel plate, the heat treatment using an induction heating device in which the target heating temperature of the steel plate after accelerated cooling is set to the magnetic transformation temperature (Curie point) of the steel material or 700 ° C. to 760 ° C. An invention to be solved by hot correction after increasing temperature uniformity is disclosed.

Japanese Patent Publication No. 06-051887 JP 2003-328039 A JP 2005-120409 A JP 2006-206927 A

  However, the invention described in Patent Document 1 discloses that the iron loss of the electrical steel sheet can be improved by applying rapid heating by electromagnetic induction heating to heating up to the Curie point of decarburization annealing of the electrical steel sheet. However, there is no disclosure of a steel material temperature control method using an induction heating device or a steel material temperature increase rate control method.

  In addition, the invention described in Patent Document 2 is intended to smoothly change the annealing condition from the preceding material to the succeeding material having different annealing conditions, and there is nothing about the temperature control method of the steel material. It is not specifically described, or nothing is disclosed about a method for controlling the rate of temperature rise of the steel material.

  Further, in the invention described in Patent Document 3, the power setting for obtaining the necessary heat-up temperature by measuring the temperature of the steel material with the thermometer installed between the inlet of the induction heating device and the induction heating device. Nothing is disclosed regarding controlling the temperature rise rate near the Curie point.

  Further, in the invention described in Patent Document 4, if the heat target temperature of the induction heating device is set to a magnetic transformation temperature (Curie point) of steel material or 700 ° C. to 760 ° C., the temperature uniformity in the steel plate is increased. Although it is disclosed that the temperature can be increased, there is no disclosure about a temperature control method of the steel material.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make it possible to heat a steel strip having a Curie point extremely uniformly in the longitudinal direction at a temperature rising rate in the vicinity of the Curie point.

  The method for continuously annealing a steel strip having a Curie point according to the present invention comprises a heating zone, a soaking zone and a cooling zone, or a heating zone, a soaking zone, a nitriding zone and a cooling zone, wherein the heating zone is a first heating zone, a second soaking zone. A continuous annealing method for a steel strip having a Curie point in a continuous annealing facility divided into a heating zone and a third heating zone, wherein the steel strip is at a temperature of 500 ° C. or higher and a Curie point Tc in the first heating zone. (° C.) In a first heating step of heating with a first heating device with a fuel gas and / or an electric heater up to below −50 ° C., and in the second heating zone, a steel strip heated in the first heating zone In the second heating step of heating by a solenoid coil type high frequency induction heating device up to a temperature range of Curie point Tc-30 ° C. to Curie point Tc-5 ° C., the third heating zone was heated in the second heating zone. Steel band with Curie point A third heating step for heating to a target processing temperature by a third heating device, and a temperature rise rate control step for controlling a heating operation in the first heating step and the second heating step, and the temperature rise rate control The step includes: a first output unit that outputs the fuel gas output value and / or the electric power output value of the electric heater to the first heating device; and a second output that outputs a current to the solenoid coil type high frequency induction heating device. A fuel gas output value output to the first heating device and / or electric power of the electric heater based on the actual output power value in the solenoid coil type high frequency induction heating device of the second heating zone. The output value is controlled.

  The continuous annealing equipment for a steel strip having a Curie point according to the present invention comprises a heating zone, a soaking zone and a cooling zone, or a heating zone, a soaking zone, a nitriding zone and a cooling zone, wherein the heating zone is a first heating zone, a second soaking zone. A steel strip continuous annealing facility having a Curie point divided into a heating zone and a third heating zone, wherein in the first heating zone, the steel strip is at least 500 ° C. and a Curie point Tc (° C.)-50 ° C. And a solenoid coil for heating the steel strip heated in the first heating zone to a temperature range of Curie point Tc-30 ° C to Curie point Tc-5 ° C in the second heating zone. Type high frequency induction heating device, in the third heating zone, a third heating device for heating the steel strip heated in the second heating zone to a processing target temperature exceeding the Curie point, the first heating device and the solenoid Coil type high frequency A heating rate control device that controls the heating operation of the induction heating device, and the heating rate control device outputs the fuel gas output value and / or the electric power output value of the electric heater to the first heating device. A first output unit that performs output and a second output unit that outputs a current to the solenoid coil type high frequency induction heating device, the actual output power value in the solenoid coil type high frequency induction heating device of the second heating zone And controlling the fuel gas output value output to the first heating device and / or the electric power output value of the electric heater.

  ADVANTAGE OF THE INVENTION According to this invention, the temperature increase rate of the steel strip in the vicinity of the Curie point of the steel strip which has a Curie point can be performed very uniformly in a longitudinal direction. As a result, particularly in continuous decarburization annealing of cold-rolled steel strips of directional silicon steel sheets that require strict control and uniformity in the temperature increase rate of the steel sheet, the temperature increase rate is achieved in a strict range. It is possible to produce a stable product with a large quality improvement effect due to uniformization.

  Hereinafter, the best mode for carrying out the present invention will be described by taking as an example the production of a grain-oriented silicon steel sheet in which the effects of the present invention are particularly significant. In addition, it cannot be overemphasized that this invention is not limited to a grain-oriented silicon steel plate.

FIG. 1 is an isometric view illustrating a schematic configuration example of a typical continuous heat treatment facility for decarburizing annealing (including application of an annealing separator) on a finish cold-rolled sheet of directional silicon steel. .
The main elements of the continuous heat treatment equipment line have a payoff reel 1 for loading and unwinding a coiled steel strip 60 of directional silicon steel that has been finish cold rolled.

  Moreover, the entrance side shearing machine 2 for cutting the tail end part of the steel strip 60 and preparing for welding, the welding machine 3 for continuously joining the end parts of the steel strip 60, and the steel strip 60 , And the inlet side storage looper 4 for storing the steel strip 60 so that the inlet side cleaning device 11 and the furnace part 12 can be passed without decelerating and stopping during welding.

  Furthermore, it comprises an inlet side cleaning device 11 for cleaning the surface of the steel strip 60 and removing dirt such as rolling oil and iron, and a heating / soaking / cooling region used for decarburizing and annealing the steel strip 60. To allow the steel strip 60 to pass through the entrance side cleaning device 11 and the furnace section 12 without decelerating and stopping when the furnace section 12 and the coil rewinding are completed and the exit side shearing machine 6 is operating. The outlet storage looper 5 that stores the steel strip 60 is provided.

  Moreover, the exit side washing | cleaning apparatus 13, the annealing separator application | coating apparatus 14, the annealing separator drying apparatus 15, the exit side shearing machine 6, and steel for washing | cleaning the surface of the annealed steel strip 60 and removing a dirt in a furnace are performed. A tension reel 7 or the like for re-wrapping the belt 60 in a coil shape is provided. Moreover, it has the temperature increase rate control apparatus 100 which controls operation | movement of the furnace part 12. As shown in FIG.

  In the continuous heat treatment equipment line constituted by such an apparatus, the annealing separator drying apparatus 15 has a highly responsive furnace structure composed of a furnace material with low thermal inertia and an open flame burner, The structure is such that the steel strip 60 can be stopped and decelerated quickly when the machine 6 is inevitable during operation.

  Further, the tension of the steel strip 60 before and after the furnace section 12 is measured by tension meters 41 and 42. Further, the tension of the steel strip 60 in the annealing separator drying device 15 is measured by a tension meter 43. The measurement results of the tension meters 41, 42 and 43 are fed back to the passing bridle rolls 23 to 26, and the tension of the steel strip 60 before and after the bridle roll is ensured. The outlet side cleaning device 13 is not necessarily installed when the steel strip 60 in the furnace section 12 is very dirty. The finished cold-rolled sheet of directional silicon steel is decarburized and annealed (including application of an annealing separator) in the above-mentioned line, then is subjected to high-temperature annealing, and is further subjected to smooth annealing and becomes a final product.

FIG. 2 is a diagram schematically illustrating a basic configuration example of the furnace unit 12.
The furnace section 12A having a basic configuration generally includes a heating area 31 (31A, 31B, 31C) by a radiant tube heating method, a soaking area 32 by electric heater heating, a nitriding area 33 and a cooling area 34 by electric heater heating. In the heating area 31, plate thermometers 36, 37, and 38 are installed for monitoring the plate temperature during heating.

  The steel strip 60 whose surface is cleaned by the inlet side cleaning device 11 is heated in the heating region 31 by the radiant tube method, heated to a decarburization temperature of about 820 ° C., and decarburized and annealed in the soaking region 32 by the electric heater heating. .

  In the heating area 31 by the radiant tube system, the steel strip 60 is heated so as not to obstruct decarburization, and a plate thermometer 36 (exit side of the heating area 31A in the first half) and 37 (center) installed in the middle of the heating area. In general, the temperature of the furnace is controlled while monitoring the plate thermometer 38 on the exit side of the heating region 31B) and on the exit side of the heating region (exit side of the latter heating region 31C). Recently, a method of automatically controlling the furnace in the heating region while automatically monitoring the measured values of the plate thermometers 36, 37, and 38 has been adopted.

  3 (a) and 3 (b), the temperature in the longitudinal direction of one steel strip coil at the position of the plate thermometers 36 and 37 in the decarburization annealing of the grain-oriented electrical steel sheet by the equipment of FIGS. An example of distribution is shown. As shown in FIG. 3, it was installed in the middle of the heating area even though a method of automatically controlling the furnace in the heating area was adopted while automatically monitoring the measured values of the plate thermometers 36 and 37. The plate temperature in the longitudinal direction of the steel strip 60 at the plate thermometers 36 and 37 varies. In particular, both ends of the coil vary greatly over a long period of time. Along with this, the rate of temperature increase of the steel strip 60 also varies greatly.

  As a result, fluctuations at both ends of the coil affect the subsequent primary recrystallization structure, and as a result, the orientation of the structure in the secondary recrystallization structure is reduced and the surface of the steel strip 60 including the decarburization reaction is reduced. This greatly affected the reaction and caused quality fluctuations in the longitudinal direction of the steel strip 60, such as magnetic defects and film defects.

The inventors of the present invention further analyzed the cause of the fluctuation of the plate temperature during the temperature increasing process in the longitudinal direction of the steel strip 60 and elucidated the following.
That is, (1) In the radiant tube furnace used for the continuous heating equipment of the steel strip 60, the steel plate is heated by radiant heat transfer between the radiant tube and the steel strip 60, and the amount of temperature rise of the steel plate is determined. The amount of heat transfer is determined by the emissivity and geometrical positional relationship of the radiant tube and the steel plate, but the emissivity and geometrical positional relationship of the radiant tube are unchanged in the short term. From this, it was clarified that the temperature of the steel strip 60 changes due to the change in the emissivity of the steel strip 60. By the way, there are many unclear points as factors that cause the emissivity of the steel sheet to change in the longitudinal direction. It is presumed that the surface properties change due to the longitudinal fluctuation of the plate temperature during hot rolling and the unevenness of the cooling process.

  Moreover, (2) Since the emissivity of a steel plate is used for the temperature measurement of a steel plate, if the emissivity changes, the accuracy of the measured value of the plate temperature will deteriorate. A plate thermometer using a plurality of wavelengths cannot be avoided from this problem, although the accuracy is slightly improved.

  As a result of intensive research, the inventors of the present invention have made a rapid decrease in the permeability of the steel strip 60 in the vicinity of the Curie point in the solenoid coil type high frequency induction heating, and the penetration depth increases accordingly. At the same time, attention was paid to the rapid decrease in the heating capacity of the steel strip 60. From this, in the heating region of the steel strip 60 including the vicinity of the Curie point, the output power of the solenoid coil type high frequency induction heating device that is energized with a constant coil current varies depending on the temperature of the coil portion inlet of the steel strip 60. Attention was also paid to the fact that the control response of the solenoid induction heating device is extremely fast.

FIG. 6 shows a basic configuration example using a high-frequency induction device.
FIG. 6 is a diagram schematically showing the configuration of the furnace section 12 of the continuous heat treatment equipment line (FIG. 1) for annealing cold-rolled directional silicon steel. Compared to the heat treatment line having the basic configuration described with reference to FIG. 2, a solenoid coil type high frequency induction heating device 35 is disposed at the center of the heating zone 31 in the furnace section 12 </ b> B of the present embodiment. Further, a plate thermometer 36 is disposed in the front part of the solenoid coil type high frequency induction device 35, and a plate thermometer 37 is disposed in the rear part.

FIG. 4 shows a control method of a basic configuration example using a high-frequency induction device.
Monitors the temperature T _A of the entry side of the sheet temperature gauge 36 of the solenoid coil type high frequency induction heating device 35,
The state of the heating area 31A by the radiant tube method is monitored.

  Further, the steel coil 60 is passed through the solenoid coil type high frequency induction heating device 35 by controlling the current value I applied to the coil so that the current value becomes a target value. The temperature gauge 37 on the outlet side of the solenoid coil type high frequency induction heating device 35 is monitored, and it is confirmed that the plate temperature of the steel strip 60 on the outlet side of the solenoid coil type high frequency induction heating device 35 is constant. The belt 60 is passed through.

  5 (a) to 5 (c), one steel strip coil measured at the position of the plate thermometers 36 and 37 on the input / output side of the solenoid coil type high frequency induction heating device 35 in the furnace section 12 at this time. An example of the temperature distribution in the longitudinal direction and the actual output power value of the solenoid coil type high frequency induction heating device 35 is shown.

  In this method, on the entrance side of the solenoid coil type high frequency induction heating device 35, although the temperature unevenness of the steel strip 60 exists as shown in the measurement data of the plate thermometer 36, as shown in FIG. On the exit side of the solenoid coil type high frequency induction heating device 35, as shown in FIG. 5B, the temperature becomes substantially uniform as measured by the plate thermometer 37.

  However, as shown in FIG. 5 (c), the actual output power value of the solenoid coil type high frequency induction heating device 35 fluctuates greatly, and the temperature of the steel strip 60 is increased in a region where the temperature increase rate needs to be managed. It was found that the speed fluctuated greatly.

  This is because, when the plate temperature meter 36 on the inlet side of the solenoid coil type high frequency induction heating device 35 has a plate temperature range of 500 to 600 ° C., the fluctuation of the emissivity of the steel plate is large, and for example, a two-wavelength measurement method with relatively good measurement accuracy. It is assumed that the measurement accuracy is not so good even if the plate thermometer is used, and that the control response of the fuel output value of the heating furnace (first heating region 31A) cannot be raised due to this. Is done.

FIG. 7 shows a control method for the high-frequency induction device according to the present embodiment.
The steel strip 60 is heated in a heating area (first heating area 31A) by a radiant tube system, the plate temperature is 500 ° C. or higher, and a predetermined temperature (Tc-50) lower than the Curie point Tc (° C.) by more than 50 ° C. Temperature).

  Then, the solenoid coil type high frequency induction heating device 35 is heated to a temperature range of Tc-30 ° C to Tc-5 ° C. Subsequently, it is heated to approximately 825 ° C. in the heating region (second half) 31C by the radiant tube method, and decarburized and annealed in the soaking region 32 by the electric heater heating.

  If the plate temperature of the steel strip 60 on the entry side of the solenoid coil type high frequency induction heating device 35 is less than 500 ° C., the required temperature increase by the induction heating device 35 becomes large. Therefore, the facility capacity of the induction heating apparatus for that purpose must be excessive, which is not practical, and when hydrogen is contained in the heat treatment furnace atmosphere, an atmosphere temperature of 750 ° C. or higher that can avoid the danger of hydrogen explosion is secured. Since it becomes impossible, it is necessary to make it plate temperature 500 degreeC or more. On the other hand, when the plate temperature is equal to or higher than Tc-50 ° C., it is necessary to make the temperature less than Tc-50 ° C. because the heating variation due to radiant heating cannot be absorbed by the ultimate plate temperature in the induction heating device 35.

  Moreover, if the plate | board temperature of the steel strip 60 of the exit side of the solenoid coil type high frequency induction heating apparatus 35 exceeds Tc-5 degreeC, the magnetic permeability of the steel strip 60 on the exit side will be too small. Therefore, the magnetic field required for the high-frequency induction heating device 35 becomes large and the required equipment becomes huge, which is not realistic. If the temperature is lower than Tc-30 ° C., the permeability of the steel strip 60 on the outgoing side is not small, and the radiant Heating variation due to heating in the system cannot be suppressed by high frequency induction heating. Therefore, the plate temperature of the steel strip 60 on the outlet side of the solenoid coil type high frequency induction heating device 35 needs to be in the temperature range of Tc-30 ° C to Tc-5 ° C.

  In the present embodiment, the solenoid coil type high frequency induction heating device is arranged so that the temperature region of the steel strip 60 requiring strict temperature rise rate control becomes the control region of the solenoid coil type high frequency induction heating device 35. Like to do.

  In the control system of the present embodiment, the steel strip 60 is passed through the solenoid coil type high frequency induction heating device 35 by controlling the current value I to be energized so that the target coil current value is obtained. And the actual output power value W of the solenoid coil type high frequency induction heating device 35 is detected, and the difference between the actual output power value and the target output power value is calculated.

Then, based on the calculation result, the set output value H of the fuel gas in the heating region (previous stage) is corrected to “H + ΔH” so that the actual output power value becomes the target value, and the fuel gas in the heating region (previous stage) The actual output value is controlled to be the set value. Incidentally, monitored at the outlet side of the sheet temperature meter 37 of the solenoid coil type high frequency induction heating apparatus 35, sheet temperature T _B of the exit side of the steel strip 60 of a solenoid coil type high frequency induction heating device 35 is confirmed to be constant The steel strip 60 is passed through. The control response of the output value of the fuel in the heating area 31A in the first half is remarkably small because the measurement error of the actual output power value of the solenoid coil type high frequency induction heating device 35 that is the basis of the control data is extremely small. Has been enhanced.

  8 (a) to 8 (c), the length of one steel strip coil measured at the position of the thermometers 36 and 37 on the entry / exit side of the solenoid type high frequency induction heating furnace 35 in the furnace section 12 at that time. An example of the temperature distribution in the direction and the actual output power value of the solenoid coil type high frequency induction heating device 35 is shown. In addition, if the plate | board temperature of the steel strip 60 of the outgoing side of the solenoid coil type high frequency induction heating apparatus 35 is less than Tc-30 degreeC, the steel strip of the inside from the fluctuation | variation of the output electric power value in the solenoid coil type high frequency induction heating apparatus 35 will be shown. Control that estimates the temperature variation of 60 and makes the output power value of the solenoid coil type high frequency induction heating device 35 constant cannot be performed effectively.

  As described above, according to the present embodiment, as shown in FIG. 8A, the measurement data of the plate thermometer 36 on the outlet side of the heating area 31A in the first half by the radiant tube method is shown in the thermometer. Although the variation in temperature of the steel strip 60 remains, it is reduced, and on the exit side of the solenoid coil type high frequency induction heating device 35, the temperature becomes substantially uniform as shown in FIG.

  Further, as shown in FIG. 8 (c), fluctuations in the actual output power value of the solenoid coil type high frequency induction heating device 35 are reduced and stable. Therefore, it can be seen that the heating rate of the steel strip 60 in the solenoid coil type high frequency induction heating device 35 is constant and stable without fluctuation.

  The directionality obtained from the fact that the steel strip 60 of the directional silicon steel sheet can be uniformly annealed in the longitudinal direction, including the rate of temperature rise, by the continuous annealing equipment of the steel strip 60 according to the present embodiment. As for the quality of silicon steel, the recrystallized structure and decarburization became uniform, the magnetism was stabilized at a high level, and the film defects were almost eliminated. Further, the number of induction heating devices is not limited to one, and a plurality of induction heating devices may be used.

  Further, the heating region (previous stage) is not limited to the radiant heating by the radiant tube method, and is effective also by the radiant heating by the direct gas heating and the radiant heating by the electric heater. In addition, although the example which has the nitriding area | region 33 was shown in FIG. 6, this embodiment is not limited to the decarburization annealing equipment of the cold-rolled grain-oriented electrical steel sheet which has a nitriding area | region, A nitriding area | region It is also effective for decarburization annealing equipment that does not have any.

  The steel strip having a Curie point to be treated by the present embodiment is not limited to the cold-rolled steel strip of the directional electromagnetic steel plate exemplified here, but a non-oriented electrical steel plate or a ferritic stainless steel plate. All steel strips having a Curie point such as cold rolled steel strip are effective.

  Moreover, as the grain-oriented electrical steel sheet containing Si ≦ 4.5 mass% to be processed in the present embodiment, for example, disclosed in JP 2002-060842 A and JP 2002-173715 A. Any component system such as a grain-oriented electrical steel sheet may be used, and the component system is not particularly limited in the present embodiment.

  In addition, as an apparatus which heats steel strip 60 to less than Tc-50 degreeC, it is not limited to a radiant tube system, The radiation heating apparatus by all the indirect gas heating or direct gas heating and / or the radiation heating apparatus by an electric heater And / or it is effective in a heating device using an induction heating device.

  Further, the method of heating from the temperature range of Tc-30 ° C. to Tc-5 ° C. near the Curie point to the processing target temperature is not limited to the electric heater heating method, and radiation by all indirect gas heating or direct gas heating is used. It is effective in a radiant heating device using a heating device and / or an electric heater. In general, Tc-30 ° C exceeds 700 ° C, and in this region, the emissivity of the steel plate increases in absolute value and is relatively less affected by the state of the plate surface. Since it becomes easy to control the temperature, the heating method is not particularly limited at Tc-30 ° C. or higher.

Next, examples of the present invention will be described.
In mass%, C: 0.05%, Si: 3.2%, Mn: 0.1%, P: 0.03%, S: 0.006%, acid-soluble Al: 0.027%, N: A steel slab containing 0.008% and Cr: 0.1% was heated at a temperature of 1150 ° C., and then hot-rolled to a plate thickness of 2.8 mm to form a steel strip coil, and thereafter annealing temperatures 1120 ° C. and 920 ° C. C. Two-stage annealing was performed. Further, after cold rolling with a reverse rolling mill to a sheet thickness of 0.285 mm, the conventional decarburization annealing equipment (FIGS. 1 and 2) and the decarburization annealing equipment of this embodiment (FIGS. 1 and 6) are used. And decarburized and annealed. Moreover, in the decarburization annealing equipment of this embodiment, it operates by both the induction heating apparatus control plan (alpha plan demonstrated in FIG. 7) and the basic control plan (beta plan demonstrated in FIG. 4) of this embodiment. did.

  Then, after performing high temperature annealing, finally smoothing annealing was performed. At that time, by measuring the temperature of the steel plate in the middle of heating with the plate thermometers 36 and 37, the variation in the plate temperature and the power output value of the high frequency induction heating device 35 is measured, and the grain-oriented electrical steel plate after the smoothing annealing. The magnetism and film defect rate were measured.

  FIG. 9 shows test conditions and test results. The start temperature of induction heating is Tc-A (° C.), the end temperature is Tc-B (° C.), and values A and B are shown in the table. In addition, as an evaluation item of the stability of the quality in the longitudinal direction of the coil, magnetism (iron loss value) and film defect rate (defect area ratio) were measured as being capable of continuous measurement (Note: Decarburization) Is difficult to measure continuously).

  In Example 1 and Example 2 of the present embodiment, there is almost no variation in the plate temperature of the steel strip 60 on the outlet side of the induction heating device, and there is almost no variation in the output power value of the high frequency induction heating device. It can be seen that there is almost no variation in the heating rate of the inner steel plate. As a result, it can be seen that the absolute value of the magnetic properties of the steel sheet is good, the variation is small, and the film defect rate is also small.

  On the other hand, in Comparative Example 11 where the induction heating end temperature was too high, the steel sheet did not reach the target temperature, and the test conditions could not be satisfied.

  Further, in Comparative Example 12 where the induction heating end temperature is too low and Comparative Examples 13 and 14 where the induction heating start temperature is high, the variation in the plate temperature of the steel strip 60 on the induction heating device exit side is not small, and the high-frequency induction downstream. It can be seen that the variation in the output power value of the heating device is not small, and the variation in the heating rate of the steel plates in the high-frequency induction heating device is not small. As a result, the absolute value of the magnetic properties of the steel sheet was low, the variation was large, and the film defect rate was high.

  Further, in Comparative Examples 21 and 22 of the control method similar to the control method of the conventional high-frequency induction heating device, the variation in the plate temperature of the steel strip 60 on the induction heating device exit side is not small, and the high-frequency wave downstream It can be seen that the variation in the output power value of the induction heating device is large and the temperature increase rate of the steel plates in the high frequency induction heating device is large. As a result, the absolute value of the magnetic properties of the steel sheet was slightly low, the variation was large, and the film defect rate was high.

  In addition, it can be seen that in Comparative Example 31 that does not use induction heating, the variation in the plate temperature of the steel strip 60 in the middle of the heating zone is very large, and the variation in the heating rate is very large. Naturally, the absolute value of the magnetic properties of the steel sheet was very low, the variation was large, and the film defect rate of the steel sheet was very large.

Next, a configuration example of the temperature increase rate control apparatus 100 that controls the operation of the furnace unit 12 will be described with reference to the block diagram of FIG.
The heating rate control device 100 of the present embodiment includes a heating gas output unit (first output unit) 101a, a current output unit (second output unit) 102, a power detection unit 103, a calculation unit 104, a correction unit 105, It has a first control unit 106a, a second control unit 106b, an output heating gas value setting unit (first setting unit) 107, an output current value setting unit (second setting unit) 108, and the like.

  The temperature increase rate control device 100 controls the heating operation of the furnace section 12, and is a device for controlling the heating operation of the first heating device 311A, the solenoid coil type high frequency induction heating device 35, and the third heating device 313A. It is.

  The heating gas output unit 101a outputs the heating gas to the first heating device 311A. The current output unit 102 sets the actual output current value of the solenoid coil type high frequency induction heating device 35 as a target output current value. The power detection unit 103 detects the actual output power value of the solenoid coil type high frequency induction heating device 35.

  The calculation unit 104 sets the target heating gas output value and the set heating gas set in the output heating gas value setting unit 107 based on the actual output power value of the solenoid coil type high frequency induction heating device 35 detected by the power detection unit 103. Calculate the difference between the output value. The correction unit 105 corrects the heating gas output value set in the output heating gas value setting unit 107 based on the difference between the heating gas output values obtained by the calculation unit 104. The first control unit 106a controls the operation of the heating gas output unit 101a so that the heating gas output value set in the output heating gas value setting unit 107 is output to the first heating device 311A.

The second control unit 106b controls the operation of the current output unit 102 so that the output current value set in the output current value setting unit 108 is output to the third heating device 313A.

Next, the operation of the temperature increase rate control apparatus 100 configured as described above will be described with reference to the flowchart of FIG.
First, in step S1101, a first heating step is performed in which the steel strip 60 is heated to a temperature range of 500 ° C. or higher and a Curie point Tc (° C.) − 50 ° C. or lower. In the present embodiment, as described above, the heating in the first heating step is performed by the heating device 311A that performs radiant heating by indirect gas heating or direct gas heating using a heating gas. The heating performed in the first heating step may be only indirect gas heating or radiant heating by direct gas heating, or radiant heating by an electric heater may be used in combination. Further, only radiant heating by an electric heater may be used.

  Next, in step S1102, it is determined whether or not the steel strip 60 has been heated to the target temperature. If the result of this determination is that the target temperature has not been reached, the process returns to step S1101 to continue heating in the first heating step. If the result of determination in step S1102 is that the target temperature has been reached, processing proceeds to step S1103.

  In step S1103, the second heating step of heating the steel strip 60 heated in the first heating step to the temperature range from the Curie point Tc-30 ° C to the Curie point Tc-5 ° C by the solenoid coil type high frequency induction heating device 35. I do. Then, it progresses to step S1104 and it is judged whether the steel strip 60 was heated to target temperature. If the result of this determination is that the target temperature has not been reached, the process returns to step S1103 to continue heating in the second heating step. If the result of determination in step S1104 is that the target temperature has been reached, processing proceeds to step S1105.

  In step S1105, a third heating step is performed in which the steel strip 60 heated in the second heating step is heated to a processing target temperature region that exceeds the Curie point Tc. Next, in step S1106, it is determined whether or not the steel strip 60 has been heated to the target temperature. If the result of this determination is that the target temperature has not been reached, processing returns to step S1105 and heating in the third heating step is continued. If the result of determination in step S1106 is that the target temperature has been reached, processing is terminated.

Next, the details of the first heating process performed in step S1101 and the second heating process performed in step S1103 will be described with reference to the flowchart of FIG.
First, in step S1201, an output current value setting process for setting an output current value output to the solenoid coil type high frequency induction heating device 35 as a target output current value is performed.

Next, in step S <b> 1202, detection processing is performed in which the power detection unit 103 detects the actual output power value of the solenoid coil type high frequency induction heating device 35 described above.
Next, in step S1203, calculation processing is performed based on the actual output power value detected by the detection processing described above. In this calculation process, as described above, the calculation unit 104 calculates a difference between the target heating gas output value and the set heating gas output value set in the output heating gas value setting unit 107.

  Next, in step S1204, a correction process for correcting the heating gas output value set in the output heating gas value setting unit 107 is performed based on the difference in the heating gas output value obtained by the calculation process described above. .

Next, in step S1205, the first control unit 106a performs heating so that the actual heating gas output value output to the first heating device 311A becomes the heating gas output value set in the output heating gas value setting unit 107. The gas output unit 101a is controlled. In addition, the second control unit 106b controls the current output unit 102 so that the actual output current value output to the solenoid coil type high frequency induction heating device 35 becomes the set output current value.
By performing the above-described processing in steps S1201 to S1205, temperature increase rate control for making the temperature increase rate of the steel strip near the Curie point constant is realized.

It is a block diagram which shows an example of the typical continuous heat processing equipment for carrying out the decarburization annealing (including application | coating of an annealing separator) of the cold-rolled sheet | seat of directionality silicon steel. It is a figure which shows typically the example of a fundamental structure of the furnace part in FIG. It is a characteristic view which shows the example of the longitudinal direction transition of the plate | board temperature of the steel strip measured in two typical places in the heating area | region of the furnace part of a basic composition. It is a figure which shows typically the basic control plan of this embodiment. It is a characteristic view which shows the example of the transition of the longitudinal direction of the sheet | seat temperature of the steel strip measured on each area | region exit side at the time of the driving | operation by the basic control method of this embodiment, and the actual output power value of an induction heating apparatus. It is a figure which shows embodiment of this embodiment and shows typically the structure of the furnace part of the continuous heat processing equipment line for annealing the cold-rolled directional silicon steel. It is a figure which shows typically the control method of the high frequency induction device by this embodiment. It is a characteristic view which shows the example of the longitudinal direction transition of the sheet | seat temperature of the steel strip measured by each area | region exit side at the time of the driving | operation by the control method of this embodiment, and the actual output power value of an induction heating apparatus. It is a figure which shows embodiment of this invention and shows a test condition and a test result. It is a figure which shows embodiment of this invention and demonstrates the structural example of the control apparatus which controls operation | movement of a furnace part. It is a flowchart which shows embodiment of this invention and demonstrates operation | movement of a temperature increase rate control apparatus. It is a flowchart which shows embodiment of this invention and demonstrates the detail of a 1st heating process and a 2nd heating process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Payoff reel 2 Entry side shear machine 3 Welding machine 4 Entry side storage looper 5 Entry side storage looper 6 Entry side shear machine 7 Tension reel 11 Entry side cleaning device 12 Furnace part 13 Entry side cleaning device 14 Annealing separator coating device 15 Annealing Separating agent drying devices 21 to 26 Bridle roll 31 Heating area 31A by the radiant tube system Heating area by the radiant tube system (heating area in the first half)
31B Radiant tube heating area (central heating area)
31C Radiant tube heating area (second half heating area)
32 Soaking area 33 Nitriding area 34 Cooling area 35 Solenoid coil type high frequency induction heating device 36, 37, 38 Plate thermometer 41, 42, 43 Tension meter 60 Steel strip 100 Temperature rising rate control device 101a Heating gas output section (first Output part)
102 Current output unit (second output unit)
103 power detection unit 104 calculation unit 105 correction unit 106a first control unit 106b second control unit 107 output heating gas value setting unit (first setting unit)
108 Output current value setting unit (second setting unit)
311A first heating device 313A third heating device T _A solenoid coil type high frequency induction heating plate of the device entry side of the steel strip temperature T _B solenoid coil type high frequency induction heating device outlet side of the steel strip sheet temperature

Claims (8)

Continuous annealing equipment comprising a heating zone, a soaking zone and a cooling zone, or a heating zone, a soaking zone, a nitriding zone and a cooling zone, wherein the heating zone is divided into a first heating zone, a second heating zone and a third heating zone A continuous annealing method of a steel strip having a Curie point,
In the first heating zone, a first heating step of heating the steel strip to 500 ° C. or more and to a Curie point Tc (° C.) − Less than 50 ° C. with a fuel gas and / or an electric heater with a first heating device;
In the second heating zone, the second heating for heating the steel strip heated in the first heating zone to a temperature range of Curie point Tc-30 ° C to Curie point Tc-5 ° C by a solenoid coil type high frequency induction heating device. Process,
In the third heating zone, a third heating step of heating the steel strip heated in the second heating zone to a processing target temperature exceeding the Curie point by a third heating device;
A heating rate control step for controlling a heating operation in the first heating step and the second heating step,
In the heating rate control step, a current is supplied to the first output unit that outputs the fuel gas output value and / or the electric power output value of the electric heater to the first heating device, and the solenoid coil type high frequency induction heating device. Controlling the second output unit to output,
Controlling the fuel gas output value output to the first heating device and / or the power output value of the electric heater based on the actual output power value in the solenoid coil type high frequency induction heating device of the second heating zone. A method for continuously annealing a steel strip having a characteristic Curie point. In the heating rate control step, a second setting process for setting a target output current value to be output from the second output unit to the solenoid coil type high frequency induction heating device in a second setting unit; A first setting process for setting a target fuel gas output value to be output to the heating device and / or a power output value for the electric heater, and a power detection process for detecting an actual output power value in the solenoid coil type high frequency induction heating device And a first correction for correcting a target fuel gas output value set in the first setting unit and / or a power output value of the electric heater based on the actual output power value detected by the power detection process. Processing and
The method for continuously annealing a steel strip having a Curie point according to claim 1, wherein a temperature rising rate of the steel strip near the Curie point is made constant.   The steel strip is heated by radiation heating by indirect gas heating or direct gas heating and / or radiation heating by an electric heater in the first heating step and the third heating step. A method for continuous annealing of steel strips having a Curie point.   The steel strip having a Curie point according to claim 1 or 2, wherein the steel strip having a Curie point is a cold-rolled grain-oriented electrical steel sheet containing Si ≤ 4.5 mass%. Continuous annealing method. A Curie point consisting of a heating zone, a soaking zone and a cooling zone, or a heating zone, a soaking zone, a nitriding zone and a cooling zone, wherein the heating zone is divided into a first heating zone, a second heating zone and a third heating zone. A continuous annealing facility for steel strips,
In the first heating zone, a first heating device that heats the steel strip to 500 ° C. or higher and a Curie point Tc (° C.) to less than −50 ° C. with a fuel gas and / or an electric heater;
In the second heating zone, a solenoid coil type high frequency induction heating device for heating the steel strip heated in the first heating zone to a temperature range of Curie point Tc-30 ° C to Curie point Tc-5 ° C;
In the third heating zone, a third heating device that heats the steel strip heated in the second heating zone to a processing target temperature exceeding the Curie point;
A heating rate control device for controlling a heating operation of the first heating device and the solenoid coil type high frequency induction heating device;
The temperature elevation rate control device is configured to supply a current to the first output unit that outputs the fuel gas output value and / or the electric power output value of the electric heater to the first heating device, and to the solenoid coil type high frequency induction heating device. A second output unit for outputting,
Controlling the fuel gas output value output to the first heating device and / or the power output value of the electric heater based on the actual output power value in the solenoid coil type high frequency induction heating device of the second heating zone. A continuous annealing facility for steel strips with a characteristic Curie point. The temperature increase rate control device includes: a second setting unit configured to set a target output current value output from the second output unit to the solenoid coil type high frequency induction heating device in a second setting unit; and the first heating unit. A first setting means for setting a target fuel gas output value to be output to the apparatus and / or a power output value of the electric heater; and a power detection means for detecting an actual output power value in the solenoid coil type high frequency induction heating apparatus. First correction means for correcting the target fuel gas output value set in the first setting unit and / or the power output value of the electric heater based on the actual output power value detected by the power detection means And
6. The continuous annealing equipment for steel strips having a Curie point according to claim 5, wherein a temperature rising rate of the steel strip near the Curie point is made constant.   The said 1st heating apparatus and 3rd heating apparatus heat the said steel strip by the radiation heating by indirect gas heating or direct gas heating, and / or the radiation heating by an electric heater, It is characterized by the above-mentioned. Continuous annealing equipment for steel strip with Curie point.   The steel strip having a Curie point according to claim 5 or 6, wherein the steel strip having a Curie point is a cold-rolled grain-oriented electrical steel sheet containing Si ≦ 4.5% by mass. Continuous annealing equipment.

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